This invention relates to a method of training a radio of a Time Division Multiple Access (TDMA) communication system. The invention is applicable to a method of providing a training sequence to train the radio.
In a Time Division Multiplex Access (TDMA) communication system, a communication channel is established having discrete time-wise subdivisions called slots which carry information. A typical channel experiences various types of interference. The interference can be xe2x80x9cwhite noisexe2x80x9d, rising and fading in the received energy of the slot transmission caused by xe2x80x9cmulti pathxe2x80x9d reception of the slots (in which the receiver receives the same slot several times).
One way in which the effect of interference is alleviated is by the use of a training sequence which is transmitted in each slot. This sequence is compared with a known sequence held in memory at the receiver and the result of the comparison is used to compensate for the effects of the transmission channel.
There are several methods known in the art for estimation, error correction and detection and for recovery symbol timing. The common methods are maximum likelihood sequence estimation or soft decision forward error correction. The methods utilise the information in the training sequence received with the slot.
One commonly employed method of finding the maximum point of a symbol involves the correlation of a known training sequence and a received training sequence. When the channel has strong xe2x80x9cwhite noisexe2x80x9d or there is fading in the channel energy then the method will find at least two maximum points for the symbol. The method will then calculate the average value between the maximum points.
The disadvantage of that method is that location of the maximum point of the symbol is not accurate and causes an error in recovering the slot information.
This invention seeks to provide a method which mitigates the above mentioned disadvantages.
According to the present invention there is provided a method to train a radio. The method is carried out in the radio and includes the following steps. A slot of information containing at least an initial portion containing training information is received. Receiving a second portion containing training information, which second portion is separated from the initial portion. Receiving a concluding portion containing training information, which concluding portion is separated from the second portion. Combining at least one of the initial portion with the concluding portion of a previous slot of information and combining one of the concluding portion with an initial portion of a subsequent slot of information to provide an at least one combined portion of training information. Using the at least one combined portion of training information and the second portion of training information to train the radio.
The invention may be, typically, implemented in a Time Division Multiplex Access (TDMA) communication system. In a TDMA system, the information is transmitted in time slots and each time slot contains a first part of a training signal of a first type at the beginning of the slot, a second training sequence of a second or third type and a training sequence from the first type in the end of the slot and by using one of the combinations of the training sequence the symbol time recovery will be improved.
In the preferred embodiment of the invention, the step of receiving a slot of information containing at least an initial portion containing training information, a second portion containing training information, which second portion is separated from the initial portion, and a concluding portion containing training information, which concluding portion is separated from the second portion comprises the step of; receiving a slot of information containing at least an initial portion containing a first predetermined number of symbols of training information, a second portion containing a second predetermined number of symbols of training information, which second portion is separated from the initial portion, and a concluding portion containing a third predetermined number of symbols of training information, which concluding portion is separated from the second portion.
Preferably, the first predetermined number of symbols is 5, the second predetermined number is 11, and the third predetermined number is 6.
In the preferred embodiment of the invention, the step of providing an at least one combined portion of training information comprises the step of providing an at least one combined portion having a number of symbols of training information that is equal to the second predetermined number of symbols.
Preferably, the at least one combined portion has 11 symbols.
In the preferred embodiment of the invention, the step of using the at least one combined portion of training information and the second portion of training information to train the radio includes the step of comparing in a predetermined manner the second portion with the at least one combined portion.
In this manner, the second plurality of values that correspond to a calculated relationship between a correlation value and an energy value includes at least one plurality of values computed for the at least one combined portion.
In this manner, the second maximum value from amongst the second plurality of values includes at least one maximum value selected from at least one plurality of values of the second plurality of values.